Albertine Donker

Iron Function and Iron Handling from Fetus to Adult 73 2 Iron and childhood The phase of childhood is characterized by a decreasing growth velocity compared to the period of infancy. The annual height velocity decreases to 8 cm (ages 2–4 years) and 6 cm (ages 4–6 year) during childhood. A plateau-like phase emerges in mid-childhood, wherein height velocity approaches 5.5 cm/year before puberty. 54 From the age of one year (infant) to 6 years (child), total body iron roughly triples from 500 mg to 1500 mg, especially due to the expanding blood volume from approximately 750 mL to 1500 mL ( Figure 1, Table 2 ). During childhood, growth largely depends on the activity of thyroid hormone and growth hormone (GH). 6,57 Noteworthy, iron is crucial for thyroid function, whereas IDA is associated with thyroid dysfunction, especially (subclinical) hypothyroidism function. 190-192 The mechanism by which iron influences thyroid function is still incompletely understood, but involves the activity of the heme-containing enzyme thyroid peroxidase (TPO), the tissue conversion of T4 to T3 and the pituitary TSH secretion. 192 A small case-control study comparing nine IDA children with matched controls showed no difference regarding TSH, FT4 and FT3 between cases and controls, and also no changes in thyroid function before and after correction of IDA in the IDA group. 193 Vice versa, GH influences iron status and distribution. 194,195 Children receiving GH treatment show decreasing serum ferritin and increasing serum transferrin levels, while Hb increases, suggesting accelerated erythropoiesis. 194 In a small study (n=15), including GH replete children and adults, GH administration decreased serum hepcidin levels, indicating that GH suppresses hepcidin production, possibly indirectly via erythropoietin induced enhanced erythropoiesis 195 However, in a next study (n=10) of the same authors, including GH-deficient adults, serum hepcidin levels did not change after correction of the GH deficit in the GH-deficient individuals. 196 However, given the small sample sizes of the above-mentioned studies, more clinical studies are required in order to explore the association between iron status and both thyroid and growth hormone in childhood. Iron and puberty During puberty, boys and girls experience a growth velocity that is greater than at any postnatal age since infancy. 6 Boys achieve a peak height velocity (PHV) of 9.5 cm/ year at a mean of about 13.5 years; the PHV in girls is approximately 8.3 cm/year at